Traders have priced in a 19.5 per cent chance of a rate increase in September and a 42.8 per cent chance in December, according to CME Group's FedWatch tool.

"The outcome of the Fed's meeting is pretty much baked into the cake today, but the language it uses may cause some movement after that point," said Mark Heppenstall, chief investment officer at Penn Mutual Asset Management.

At 9:38 am ET the Dow Jones Industrial Average was up 59.99 points, or 0.32 per cent, at 18,533.74.

The S&P 500 was up 3.38 points, or 0.16 per cent, at 2,172.56.

The Nasdaq Composite index was up 32.44 points, or 0.63 per cent, at 5,142.49.

Of the 157 S&P 500 companies that have reported results so far, 69 per cent have topped earnings estimates. In a typical quarter, 63 per cent of companies beat expectations, according to Thomson Reuters data.